The role of photo-electric properties of silk cocoon membrane in pupal metamorphosis: A natural solar cell

Abstract

Silkworm metamorphosis is governed by the intrinsic and extrinsic factors. One key intrinsic factor is the temporal electrical firing of the neuro-secretory cells of the dormant pupae residing inside the silk cocoon membrane (SCM). Extrinsic factors are environmental like temperature, humidity and light. The firing pattern of the cells is a function of the environmental factors that eventually controls the pupal development. How does the nervous organization of the dormant pupae sense the environment even while enclosed inside the cocoon shell? We propose that the SCM does this by capturing the incident light and converting it to electricity in addition to translating the variation in temperature and humidity as an electrical signal. The light to electricity conversion is more pronounced with ultraviolet (UV) frequency. We discovered that a UV sensitive fluorescent quercetin derivative that is present on the SCM and pupal body surface is responsible for generating the observed photo current. Based on these results, we propose an equivalent circuit model of the SCM where an overall electrical output transfers the weather information to pupae, directing its growth. We further discuss the implication of this electrical energy conversion and its utility for consumable electricity.

Water mediated dielectric polarizability and electron charge transport properties of high resistance natural fibers

“…The recent experiments on the most abundant natural fibers from insect, animal and plant kingdom 22 – 26 viz., silk cocoon ( Bombyx mori , Antheraea mylitta ), human hair, jute and corn-silk (obtained from the corn cob of the maize plant) show that at optimum moisture, temperature and light conditions, these fibers exhibit thermoelectric, photo-electric and magnetic properties 1 , 2 , 27 , 28 . However, the nature of charge carriers and the effect of water (if any) on the charge transport properties of these fibers, have not been explored.…”

Soft magnetic memory of silk cocoon membrane

“…Successful metamorphosis of dormant pupae to an adult moth is function of temperature, humidity, light, UV protection, water proofing, gaseous balance and physical protection from the predators 1 2 3 4 5 6 7 8 9 10 11 12 . To meet these requirements, nature evolved a ‘robust growth incubator’ in the form of ‘silk cocoon’, which is equipped with moisture, heat and light sensor 1 2 3 5 . Studies have confirmed that SCM converts photons, especially in UV range, to generate electricity 1 .…”

“…To meet these requirements, nature evolved a ‘robust growth incubator’ in the form of ‘silk cocoon’, which is equipped with moisture, heat and light sensor 1 2 3 5 . Studies have confirmed that SCM converts photons, especially in UV range, to generate electricity 1 . Similarly in presence of moisture, heat energy is converted into electrical signals by SCM 2 3 .…”

“…Similarly in presence of moisture, heat energy is converted into electrical signals by SCM 2 3 . These electrical currents direct the growth of pupae probably by providing information about the external environment 1 .…”

“…But is it electricity alone? The pupae tends to stay inside the SCM for varying periods of 21 days to 9 months, depending on the species 1 5 12 . For the dormant pupae to survive this changing weather conditions, the ‘silk cocoon incubator’ may require an ‘ inner memory ’ so as to stabilize against the varying electrical current.…”